This invention relates to a method for the manufacture of an activated carbon by using as the starting material therefor a polymer containing polyacrylonitrile and to an activated carbon manufactured by said method, which activated carbon contains nitrogen as part of the molecular structure thereof.
Textile products for clothes and the like which use, as their starting materials, polyacrylonitrile resins or copolymers of acrylonitrile are produced in great quantity and polyacrylonitrile-containing industrial wastes from their production processes occur in huge quantities. Heretofore, these industrial wastes have generally been disposed of by incineration. The activated carbon according to the present invention can easily be manufactured from these industrial wastes. Thus, the present invention offers an advantageous use for otherwise worthless industrial wastes.
As is universally known, when a polyacrylonitrile is heated to a temperature over 200.degree. C. in the air, it first undergoes discoloration to a black shade and eventually converts itself into a thermally condensed (thermally decomposed) polymer having a structure containing therein a pyridine ring. This thermal condensation product offers resistance to heat and fire such that it remains intact even in a flame. It is known that when this product is left to stand in a flame for a long time, it remains incombustible, though it may suffer loss of strength. With a view to utilizing this thermal behavior to advantage, attempts have been made to manufacture a carbon fiber by heating this thermal condensation product to a temperature above 1000.degree. C., preferably above 2000.degree. C., in an inert gas such as nitrogen etc.
The carbon fiber thus produced contains little nitrogen (about 3% at the most) and is a graphite structure of small surface area which, although of high strength and elasticity, possesses little absorptivity.
In contrast, the activated carbons now in widespread use are manufactured by carbonizing vegetable substances, coal, animal bones, etc. and subsequently activating the carbonization products. Thus, they are substantially composed of carbon. They contain hetero-atoms such as oxygen, nitrogen, sulfur and phosphorous only in negligible percentages. Negligible as their percentages may be, there is a possibility that these hetero-atoms will have an appreciable effect on the properties of the activated carbons. This possibility is evidenced by a report that the activated carbon produced from bone black as the starting material exhibits a high adsorbing property for heavy metals because it contains phosphorus. It has also been established that any conventional activated carbon, when it is prepared so as to incorporate a nitrogen-containing compound, shows much greater adsorbing capacity for certain kinds of heavy metals than when it is prepared without such addition.
The present inventors noted and took special interest in the high thermal stability displayed by the thermal condensation product of polyacrylonitrile and copolymers thereof and have found that activation of this thermal condensation product brings about an activated carbon which is considerably useful, and consequently they have accomplished the present invention.
A primary object of the present invention is to provide an activated carbon which is produced from an acrylonitrile-containing polymer as the starting material and which, therefore, contains nitrogen in the molecular structure thereof and enjoys an outstanding capacity for adsorbing mercaptans in particular.